In order to obtain three-dimensional information from a plurality of images captured from a single viewpoint, a method has been proposed in which extended depth of field (hereinafter, “EDOF”) is combined with a scene depth measurement technique.
Various methods have been proposed as schemes for realizing extended depth of field (hereinafter referred to as “EDOF”). For example, a method has been proposed (Non-Patent Document 1) for performing a focus sweep operation of moving the focus lens or the imaging device during the exposure time, for example, and convoluting an image that is uniformly focused in the depth direction (which is equivalent to making the blur uniform across different depths), obtaining an EDOF image by performing an image restoration process using a blur pattern obtained in advance through a measurement or simulation. This method is referred to as flexible DOF (hereinafter referred to as “F-DOF”).
F-DOF is known as a scheme capable of obtaining a good image quality, and also has a high EDOF effect. Since the off-axis characteristics are also dependent on the lens characteristics themselves, it is possible to easily enhance the performance. Note however that since it is necessary that the same object is convoluted onto the same image position even if the focus position is moved during exposure, it needs to be an image-side telecentric lens as an optical condition.
One field in which the EDOF technique is applied is microscopy. When capturing an image with a microscope, the object to be captured is a stationary object, and therefore it is possible to use some time to capture an image. Therefore, the focal stack scheme has long been used. In this scheme, a plurality of images of different focus positions are captured, and different areas believed to be in focus are extracted from the images and synthesized together, obtaining an EDOF image. Since these operations require labor and time, techniques have been proposed in which the F-DOF scheme is also used in combination (Patent Document Nos. 1 to 4). Where F-DOF is used in a microscope application, the sample, which is the object, or the lens barrel is used during the exposure. Where it is assumed that a post-exposure image restoration process is performed, the object or the lens barrel is moved so that the blur of the image is always uniform. It has been known that appropriately controlling this manner of movement is practical because it is then possible to use an image restoration process method using a single blur pattern (Patent Document No. 5). For this purpose, when the imaging device is moved, the imaging device is moved at a uniform velocity. Where the focus lens is moved, it is necessary to realize displacement of the focus lens that is equivalent to the image capturing surface moving at a uniform velocity (Non-Patent Document No. 1). It is known that the pattern of movement may be from the far-side focus end position to the near-side focus end position, or the opposite thereto.